backfire through carb, ignition problem?

Alright, I've been playing with this off and on for about 4 months now. I have an 87 roller 5.0, stock cam, stock heads, stock non-adjustable rocker arms, Mallory dual point distributor. Timing is correct 13726548 for roller 302. I'm trying to start the engine and it keeps backfiring through the carb, and then I get flame on top of the carb. It seems like I'm running too far advanced but I've played with the timing so much. I even removed a valve cover to make sure my rotor was hitting the dist cap at the right spot. Or, it also is like my valves aren't closing all the way. Is that possible with the stock pedestal mounted rockers? Since, I've replaced the spark plugs, dist condensor, made sure I wasn't 180 degrees off on timing, I checked the carb, accelorator pumps are fine, squirters fine, float levels fine, power valve fine. I even swapped carbs with a car I was driving today that ran fine, same backfire through the carb and flames. So I'm sure its not a fuel issue. I am almost sure it is ignition. Any ideas?

351carlo said:

While you said you checked for 180 out.... we all make mistakes. Try and move it 180 out of where you have it now, and tell us the results. It is very possible to get confused on the stroke that the motor is on, and assume it is TDC when it is 180 out.

Aside from that, backfiring through the carb means timing. You really need to check your wires one more time, and try to flip the distributor. I've made the mistake enough times to know it's easy to make.

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For the 180 out, here's what I did to make sure I wasn't:
I was turning the crank by hand, watching the intake valve on the #1. I removed the #1 plug and help a screwdriver in there. After the #1 intake valve went down and up, I kept turning the crank until the screwdriver topped out TDC. I was turning the crank clockwise, watching the rotor turning counter clockwise. I have the rotor hitting the #1 wire on the cap. I have the plug wires in the 13726548 order, made sure it was counter clockwise pattern on the cap also.
If its timing, wouldn't backfiring through the carb mean it was too advanced? I will play with it some more. I can't get the engine to turn over enough to check anything. I get it to crank over maybe half a rev. and the flame comes and then I have to get out and put it out. I have done this over and over again at different degrees of timing and get the same results. I tried a balast resistor today with no change. I am thinking its the dual points now. Maybe they are misgapped.
Thanks for all the replies, I'll keep posting until I figure it out.

66Runt said:

Have you tried the non-roller firing order 1,5,4,2,6,3,7,8?
Not all late model engines were rollers. Truck block 302s were not rollers and used the old style firing order up past 88 (not sure when they stopped that nonsense), but the blocks show late model year codes.

It's pretty easy to swap the plug wires around to check.

Another thought is to make sure the points just start to open when the rotor tip is about a quarter to third of the way into the number one tip on the cap, and the timing marker is about 8 degrees. If your points are fully open at 8 degrees you are way to far advanced.

Keep us posted! and good luck,

Scott

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Thanks for the tip Scott. I installed the roller cam, with all the roller gear. Bfore anyone wants to get deep into this, I would just like to say, I did research this when making my 351w a roller engine and did know what I was doing this time on assembly.

I'll pay more attention to the timing as you described it. I think I fried my starter in the past few days of cranking it. I was mean to it, so I need to fix that before I can move forward. I'll keep everyone posted, be back in a few days.

Scott,

You might be onto something with the firing order. Someone mentioned something interesting to me recently. They said not all roller cams had the 13726548 firing order. Some non-ho roller cam equipped 5.0 engines had the 302 15426378 firing order. If this is the case then I'm not exactly 180 out, just 180 out on the middle two strokes of a revolution of the crank. And, if this is the case, then I have been wrong about the firing order being wrong, which many have been saying since the beginning. I will get back sometime this week and let everyone know if I'm a dumbass, or if I'm still having a backfire issue.

Thank you all for the great support. I try to do the same where I can.

Bart